We continue to keep a close eye on Friday as it looks like it could be a slick one out there. The latest 00z NAM model data has increased the freezing rain potential from central Iowa and to the points southeast. There are a few things that are complicating the forecast.
The first item that we will look at is the sounding from the 00Z NAM run in Des Moines. As you can see the upper levels the atmosphere are cold enough to support snow, but then the precip will fall through the warm midlevels and will change any frozen precip back into liquid. However, near the surface, temperatures are right at freezing or slightly above and this would lead to freezing rain. So according to the NAM, this could lead to a significant icing event. The 18z NAM tried to bring wrap around moisture, where that would occur in the cold sector so that translated to snow, but this has since corrected itself and not much snow is expect according to the NAM.
The GFS run is making this a very difficult forecast. In the southeast corner of the state, soundings are warm enough for all rain, however the further north you go, the colder it gets so more snow is expected. Right now it is hard to pin point down exact locations that will see freezing rain, however, the chance is there but we will have to continue to keep an eye on this over the next few runs to get a better idea on who well see freezing rain and who will see snow. Right now the weather prediction center has the southeast quadrant of the state in a 90% probability of ice accumulation of 0.01” or grater. Once we get closer to the actual event, and confidence increases, would not be surprised to see this increased as it stands now. Like always we will continue to track the very latest and will bring those updates right here at iowachase.com.